The RP xp is more of an incentive; what I've got is a party of newer players with a tendency to ignore anything they can't hit with a sword, and I'm looking to put a bit of carrot there to get them into role-playing in general; I've also taken steps to make sure my quieter players have some time in the spotlight. For example, my last session the two louder players ended up getting drunk and were stuck in bed with a hangover the next morning, giving the quieter two time to encounter an NPC who presented a task to the party.
I will have to watch that the louder characters don't out-level the quiet ones simply by virtue of being louder naturally, however I do want some gaps in XP.
I'm still unhappy with the encounter system improperly scaling for multiple creatures and want to hear if anyone has come up with a solution. I mean, the reality is that APL doesn't even really adequately guage a party's strength, as a party of level 1 NPC clones would be a CR 5... but that's clearly too high for level 1's to fight, right?